Large efforts have been invested in changing the ways that vacuum is controlled in milking machines. This far, however, these efforts have not resulted in a commensurate improvement in milking performance.
One problem when controlling the vacuum in a milking machine is that the vacuum level at the teat end differs from the system vacuum (i.e. pump vacuum or a controlled constant vacuum below pump vacuum), and that the difference varies with time during milking, which result in difficulties to predict how the teat and vacuum is affected by a change in system vacuum.
The difference between system vacuum and the vacuum level at the teat end is mainly the result of a vacuum drop in the long milk tube and the associated vacuum fluctuations caused by slugs of milk in the tube and intermittent air admission to the milking unit, a vacuum drop and vacuum fluctuations produced in the short milk tube due to milk slugs, vacuum fluctuations at the teat end caused by the opening and closing of the liner, and slugging in the milk line.
In order to control the teat end vacuum several designs have been implemented that includes separating milk and air flow near the milking animal, reducing the amount of undesired air admission to the vacuum system, increasing the diameter of the short milk tube, the long milk tube, and the milk line, and reducing teat end vacuum during periods of low milk flow.
There are two fundamental methods of influencing the vacuum in the milking machine: 1) using a vacuum pump running at constant speed, and a device to regulate the vacuum based on adjustment, of the amount of air being admitted to the milking machine, and 2) using a control device to regulate the vacuum based on adjustment of the amount of air being removed from the milking machine, i.e. using a variable frequency drive (VFD) controller for adjusting the vacuum pump speed.
Common vacuum regulation devices based on the first method include those relying on a force balance between the partial vacuum produced inside the milking machine and the resisting force of a weight, spring, or similar. More sophisticated regulators use a feedback system consisting of a sensing element and a mechanical amplification system. A small control valve regulates the movement of a much larger air inlet valve.
U.S. Pat. No. 6,164,242 discloses a milking apparatus which includes a vacuum pump, a milking device having at least one milking claw and teat cups provided to be attached to an animal to be milked, and a conduit connecting the milking claw and teat cups to a suction side of the vacuum pump and being adapted to transport a flow from the milking device. The vacuum pump is of a dynamic type. Furthermore, a regulating device is adapted to maintain the vacuum level of the milking apparatus at a desired, constant value. Furthermore, the regulating device comprises a sensor for sensing the actual vacuum level to the desired value by regulating the size of the air flow through the conduit and the vacuum pump in response to the vacuum level sensed.
U.S. Pat. No. 6,494,163 B1 discloses a vacuum control system comprising a vacuum pump which is interconnected to a buffer vessel via a vacuum line. Each teat cup of the milking apparatus has a milk line which interconnects the teat cup to the buffer vessel. A regulator which includes an rpm governor and an electronic filter unit is connected to the vacuum pump and also by the filter unit to a vacuum sensor which, in turn is connected to the vacuum line. The filter unit is connected both to the rpm governor and to an electronic fast-acting control valve which is activated by the regulator on the basis of signals which it receives from the vacuum sensor. If the vacuum decreases in the vacuum line (and thus the buffer vessel) as result of, for example, a teat cup being disconnected from the teat of an animal being milked, the rpm governor causes the vacuum pump to increase its rpm and therefore capacity whereby the vacuum is maintained at a constant value. On the other hand, if the vacuum in the vacuum line increases over its desired level, the electronic fast-acting valve is actuated to admit air to the vacuum line and thereby maintain the vacuum therein at a constant desired level.